The present embodiments relate to calibration of computed tomography (CT) systems. For consistent high image quality, CT scanners perform an “air-calibration” scan typically once a day. For the air-calibration, no objects are in the beam during the scan. Certain electrical and optical components in the CT detector system (e.g. photodiodes, scintillators, op amps, etc.) are sensitive to “gain drift,” or have gain and offset values that are only suitable for a range of operating conditions. The CT system has a different gain calibration number for each detector channel (of which there can be thousands of channels). Without recalibration over time or change in environment, the gains may be incorrect, and this “gain drift” may result in unpleasant or unacceptable artifacts in the CT image. For example, a “ring”, “partial ring”, or “dagger” artifact results for sub-optimal gain calibration.
To prevent artifacts, an air-calibration is recommended to be performed at least once a day, once per shift, and/or whenever large environmental changes (e.g. in temperature) are experienced. The air-calibration consumes time and is done for all x-ray voltages, focal spot sizes, and x-ray filters. Calibration is also important in the case of mobile CT scanners, which operate in different environmental conditions due to their mobile nature.
For consistent image quality in a mobile CT scanner, air-calibration prior to every patient or at every differing location may be advised. Although no object/phantom needs to be placed in the CT scanner, air-calibration is initiated manually. As a result, air-calibration may not occur when appropriate. The recommended times may not be used and/or may not be appropriate for a given situation. Additionally, especially for mobile CT scanners, for which there is no control room or exam room, air-calibrations potentially result in scatter radiation exposure outside the scanner.